(a) Field of the Invention
This invention relates to an improvement in the wet milling process for separating and recovering the various constituents (primarily starch, gluten and oil) from cereal grains, the two cereal grains most commonly processed by means of the wet milling process being corn and "milo", also known as grain sorghum (the scientific name being Sorghum vulgare, of the family Gramineae). More specifically, the present invention relates to an improvement in the steeping step of the wet milling process, whereby the steeping step is considerably shorter than in the conventional process and the lactic acid content of the steep water is increased.
(B) Description of The Prior Art
The wet milling process is an old and well known industrial process, and is fully described in the published literature. For detailed information on the process, reference may be made, for example, to either of the following two publications: (1) the chapter entitled "Starch", by Stanley M. Parmerter, contained in Volume 18 of Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Interscience Publishers, a division of John Wiley & Sons, Inc., New York, London, Sidney, Toronto (1969), and (2) the chapter entitled "Manufacture of Corn and Milo Starches" by Stanley A Watson, appearing in Starch: Chemistry and Technology, Volume II Industrial Aspects, edited by Roy L. Whistler and Eugene S. Paschall, Academic Press, New York and London (1967).
In the manufacture of starch by means of the wet-milling process the grain, after preliminary cleaning to remove foreign material, is almost invariably steeped for a period of about 36 to 60 hours (most commonly, for a period of from 40 to 50 hours) in warm acidulated water at about 50.degree. C, having a concentration of sulphur dioxide of about 0.15%. Parameters which have a positive effect on the grain steeping step of the corn wet milling process are: concentration of sulphur dioxide, steeping temperature and time. With the increased disintegration of the protein network the endospern is softened and the water penetration in the grain is achieved. It is well known in the art that during the steeping process the protein network swells and tends to form a large number of swollen globules of hydrated proteins.
As the conditions during steeping, (i.e., temperature, pH, and soluble carbohydrates) are favorable for the development of lactic acid bacteria, they grow at a very fast rate adsorbing and eliminating other microorganisms. The opinion that the formed lactic acid influenced the protein degradation has proven to be erroneous. Also the addition of acids, including lactic acid does not appear to improve the steeping process anymore than distilled water.